Enteral administration of alanyl-[2-(15)N]glutamine contributes more to the de novo synthesis of arginine than does intravenous infusion of the dipeptide in humans.

BACKGROUND

We previously confirmed in humans the existence of a pathway of glutamine into citrulline and arginine, which is preferentially stimulated by luminally provided glutamine. However, because glutamine is unstable, we tested this pathway with a stable dipeptide of glutamine.

OBJECTIVES

The objectives were to explore whether alanyl-glutamine contributes to the synthesis of arginine in humans and whether this depends on the route of administration.

DESIGN

The study was conducted under postabsorptive conditions during surgery. Sixteen patients received alanyl-[2-(15)N]glutamine enterally or intravenously together with intravenously administered stable-isotope tracers of citrulline and arginine. Blood was collected from an artery, the portal vein, a hepatic vein, and the right renal vein. Arterial and venous enrichments and (tracer) net balances of alanyl-glutamine and glutamine, citrulline, and arginine across the portal-drained viscera, liver, and kidneys were determined. Parametric tests were used to test results (mean +/- SEM). P < 0.05 was considered significant.

RESULTS

Twice as much exogenous glutamine was used for the synthesis of citrulline when alanyl-glutamine was provided enterally (5.9 +/- 0.6%) than when provided intravenously (2.8 +/- 0.3%) (P < 0.01). Consequently, twice as much exogenous glutamine was used for the synthesis of arginine when alanyl-glutamine was provided enterally (5 +/- 0.7%) than when provided intravenously (2.4 +/- 0.2%) (P < 0.01). However, results at the organ level did not explain the differences due to route of administration.

CONCLUSIONS

Alanyl-glutamine contributes to the de novo synthesis of arginine, especially when provided enterally. A stable-isotope study using a therapeutic dose of alanyl-glutamine is needed to investigate the clinical implications of this finding.